In recent years, electrical stimulation has been used extensively in clinical rehabilitation settings where patients demonstrate difficulties with voluntary movement. Application of an electrical field transcutaneously to an innervated muscle produces excitation of a motor unit (i.e., nerves and muscle fibers innervated by that nerve). This ability to excite immobilized muscles has numerous reported benefits including the reduction of atrophy, reduction of post-op rehabilitation time, correction of contractures, facilitation of voluntary motor function, maintaining ranges of motion, avoiding adhesions, increasing muscle bulk, reducing swelling, relieving pain, and improving fatigue resistance. While such devices have been found beneficial, the results have been somewhat inconsistent.
Numerous devices and methods of applying EMS are readily available. Generally these muscles stimulators use comparatively long "on" periods of stimulation and short "off" periods of non-stimulation which overstimulate the muscles. Known commercially available stimulators are typically only used for relatively short periods of between 15 minutes and a few hours each day without patient discomfort, muscle fatigue, and muscle atrophy. Such stimulators have been built on the theory that in order for muscles to be built up, the muscles must first be exhaustively stimulated. A multitude of diverse and disassociated treatment regimens using this theory have produced stimulators with widely varied stimulation parameters. The relevant parameters are current or voltage amplitude, pulse duration, frequency of the pulse, on versus off duty cycles and wave forms. Optimum application of these parameters has not previously been discovered.
Duty cycles in most stimulators are capable of variation by the operator or patient based on personal preference rather than knowledge as to the optimum stimulation parameters necessary to enhance fracture healing and muscle maintenance. It has been found that commercially available stimulators have on periods of stimulation in duty cycles which are typically too long or off periods in duty cycles which are too short. Such stimulators consequently have produced mediocre and mixed results in clinical application.
Little basic research relating bio-energetic demand to voluntary or EMS induced muscle exercise has been conducted. Research has been limited by the time-consuming and destructive means of monitoring cellular metabolic demand through muscle biopsies. However, Phosphorus Nuclear Magnetic Resonance (31/P-NMR) spectroscopy has recently been used for non-invasive monitoring of several important metabolic parameters of muscle exercise including high energy phosphates (ATP) and phosphocreatine (PCR), inorganic phosphate (P.sub.i), and sugar phosphates. Britton Chance has reported that exercise causes breakdown of PCR and concomitant increases in P.sub.i resulting in a decrease of PCR/P.sub.i monitored by 31/P-NMR analysis. (See, B. Chance, Non-invasive, Non-destructive Approaches to Cell Bio-Energetics, Proc. Natl. Acad. Sci. U.S.A., 77:12, 7430-34, 1980.)
Prior effects to utilize electrical stimulation to treat muscle and bone irregularities include a family of patents by Ryaby et al. U.S. Pat. No. 4,105,017 is directed to a method of inducing patterns of electrical charge in a magnetic field. U.S. Pat. No. 4,315,503 is directed to a device for producing particular patterns of electrical voltage and current. U.S. Pat. Nos. 4,266,532 and 4,266,533 are directed to body treatment devices for applying electrical charge. These patents disclose the use of sequential electric charges in particular wave forms designed to control the behavior of non-excitable cells involved in tissue growth, repair and maintenance. The method utilizes a pattern of electrical charge from a stimulator to create a magnetic field with duty cycles in the range of 1% to 30% combined with on periods of stimulation as high as 5 milliseconds.
Axelgaard, et al. discloses in U.S. Pat. No. 4,326,534 and U.S. Pat. No. 4,342,317 method and apparatus for applying electrical muscle stimulation for the treatment of scoliosis and other spinal deformities. The method utilizes a pattern of electrical charges alternately applied to muscle groups on opposite sides of the deformity. The pattern of electrical charges represents a square wave with a preferred duty cycle of 25% and variable on/off periods between 4 and 40 seconds.
Kraus also provides a method and apparatus, U.S. Pat. Nos. 3,783,880 and 3,918,440, respectively, intended to aid the formation of bone forming material by electrical stimulation. The method utilizes a charge which is applied continuously at a specified current density and frequency.
The methods and associated charge generators disclosed by these patents either inadequately stimulate muscles by providing on periods of charge of insufficient duration or do not allow stimulated muscles sufficient time to relax during the off period after each electric charge. The prior art does not teach or provide sufficient stimulation and consequent substantial relaxation of muscles to prevent muscle atrophy and enhance fracture healing.
A number of muscle stimulators are commercially available which attempt to exercise muscles to prevent atrophy and encourage bone formation. A representative device is marketed under the trade name Zimmer "R" by Zimmer U.S.A., of Warsaw, Ind. U.S.A. The Zimmer stimulator provides duty cycles which can be varied between 10% and 90%; on periods of stimulation which vary between 3.5 and 34 seconds; and off periods of stimulation which vary between 10 and 225 seconds. This stimulator suffers from the same shortcomings of prior patents in that known methods of its use do not contemplate or teach optimum periods of muscle stimulation and rest required by the method of the present invention.